Computer users normally depend upon a local electric utility company to provide energy that is within a specified voltage range. When the voltage deviates from this range, even briefly, many computers follow an orderly shut down procedure. Shutting down results in lost work time for the operator.
Devices are known which monitor the power supplied to the computer and initiate a shut down procedure when the supply voltage reaches a certain value, the AC low voltage. The monitor outputs an AC low signal to the computer when the AC low voltage is reached. Once this AC low signal is asserted by the monitor, the shut down procedure is begun, and the known devices cause the computer to stop processing and to perform housekeeping functions which prevent a significant loss of information.
The vast majority of voltage supply problems are of short duration, on the order of 100-500 msec. By providing a device which allows the computer to ride through a short duration voltage supply problem, the initiation of the shut down procedure would be avoided in most instances However, when the problem persists beyond the short duration, the shut down procedure should be initiated.